Frequency translating circuits



Filed Jan. 31-, 1927 low M0 [@Qow 4071/41. I

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fomey defined. for the purpose, ofthis specification "prevent one. type of-modulation when the UilTE a S Ares Patented Jan. 29,1929.

CLYDE R. K ITH, OE-NEW YORK/N. -Y., Assreiroacno BELLwTELEPH'O-NE, LABORA-.- roams NcoRPoRArED, or NEW YORK, 1v; Y., AcoaroRATIoit or NEW-YORK;

rREouENcY TRANSLA ING cinemas.-

' Application filed January 31, 19271 Serial no} 164394;

' inventionrelates to frequency translatingigcirc uits and particularly tosuch circuits employing electric discharge devices in the] input circuit of which the frequency translation takes place, for example grid current modulation in the grid circuit of a threeelectrodevacuumtube.

' An object of this invention is to improve icui'tsf Av further object of the invention is to "prevent. output current modulation or detection in frequency. translating circuits-of theinput the efliciency of frequency translating cir I current. modulation or. detection type;

Frequency translating circuits, which are as including both modulators and demodulators or detectors, may employelectric discharge devices for performing the frequency translation functionin which case they may (be divided into two main 'typesi the input circuit frequency translation, or, as more commonly; known the. grid current modulation, type, in which the. combination is produced in the, grid or input current clrcuitand .is due to the curvature of'the grid current characteristic; and the output current. frequency translation, or as. more commonly knownthe plate current modulation, type, in which the combination is produced in the plate or output circuit and is due to the curvature of the plate current characteristlc.

' The products resulting from these two types of. modulation or detection may be of ,oppositephase so that. it is often desirable to other is being used to produce auseful output -When input current modulation or detection is used for producing. the useful. output 7 products, the discharge device. acts as aniam- --plifier for. the modulation. products produced inthe input. circuit. However, the discharge 7 device may operate to also transmit the un- 1 i accordance with this invention there is combined waves tothe output circuit where theymay beycombined' to produce output L modulation or detection products which, as

- stated above, maybe ofi'oppo'site phase to the modulation products produced by the input current,

E or; FICE, I i

provided a circuit u rangementfor"increasmg theumpedanceof the output circuit'to uncomb ned waves to prevent output current modulation or detection in a circuit produc-, mg grid-current modulation products.

Ina preferred embodiment this invention. comprises a balanced input current modular being low to give the output circuit a high impedance-to the'wave impresse dfupon the common input branch, and having ajfilter or otherimpedance network connectedin the output circuit',the networkbeing so designed'as to give the output circuit a high impedance to the waveim ressed upon-the individual input branches. y means ofthisarrangement the impedance of the output circuit is made high for both of the uncomhined Waves and" out i put current modulation nated. I

i This invention-is not limited to the'combin'ation of these features. [In practiceit'may befound that the use ofthe special output transformer having low mutual inductance between theportions ofj theprimary winding will produce suflicient efiect to reduce the plate current'modulation to a-practically negligible value. In other cases'it may be desirableto merely use the filter or other impedancenetwork, In soineftypes of circuits such a 'networkmay be designedtogive the output circuit ahigh impedance to looth of the'uncombinedwaves.-

is substantiallyelimi- I This invention is 'illustratedin the accom- 1 panying drawing'in which:

Fig. 1' shows diagrammatically an einhodi-Z ment of the invention employing anoutp'ut' transformer having low mutual inductance between the portions of'the primary wind; g f l i Fig. 2 shows an embodiment of the inveny tion'employinga filter having such iinpedance characteristics as to prevent platecur rent modulation; and

' Figs. 3 and 4 show typical filter sections which are well adapted for use in the circuit of Fig. 2.

In the circuit of Fig; 1, two electric discharge-devices 10 and 11 are connected in push-pull relation between an input transformer 12 and an output transformer 13. Signaliwaves to be modulated or demodulated are supplied through the input transformer 12. Carrier waves from a source 14 are supplied to the input circuit through a transformer15 connected in the commoninput branch.

The signal and carrier waves are combined in the input circuit of-th'e devices 10 and 11 to produce grid current modulation'products,

' in the manner described in the application and the impedance.

of E. PetersomSerial No. 696,766, filed March 4, 192 1, by includingin the input circuit an impedance of such value that when the grids are positive the greater part of the potential drop takes place across this impedance while during the negative portion of the cycle the potential drop divides'between the devices In the circuit shown hereinthesecondar winding of the transformer 12 is designer to act as this impedance. The grid current modulation products are amplified by the devices 10 and 11 and transmitted tothe load circuit: through the output transformer 13. The couplingbetween the'primary windings 16 and 17 is made low charge'devices 10 and 11 are similarly ar-' ranged to produce grid current modulation which gives-the same effect as though an inductance coil 18 were connected in the common output branch. In this waythe output circuit is given a high impedance to the carrierw ave impressed upon the common input brairch'and plate current modulation is suppressed, while the'transmission of the grid current modulation products is practically unaffected. In the circuit of Fig.

2 the electric disproducts which are amplified by the devices andtransmitted through the output transformer 13 and the filter 20 to the load circuit.

' As in the circuit of Fig. 1 the transformer 13 isdesigned tohave low mutual between the primary windings to give the output circuit a high impedance tothe carrier wave. .The

filter 20 is so designed that it gives the output circuit a high impedance to the signal waves whilepermitting the modulation products to be efficiently transmitted. 7

Fig. 3 shows a low pass filter section well suited for use in the filter 20 when the circuit f is used as a demodulator. This section comprises a series inductance 21 and a shunt condenser 22 and b terminatm the side ada y a:

' jacent the output transformer 19 in a series 'arma high impedance is offered towaves of I frequencies above the cutoff.

Fig. 4 shows a band ass suited for use in the lter 20 when the cirfilter sectionfwell 7 cuit is used as a modulator. This section comprises a resonant circuit 23 in the series arm and an anti-resonant circuit 24 .in the shunt arm. By terminating the side of the filter adjacent the output transformer in a waves outside the transmission band.

In an unbalanced circuit the filter or net work maybe vdesigned to give the output'circuit a high impedance to both of the uncombined waves; 7. v.

series arm a high impedance is offered to primary winding connected between :the

anode and cathode of each of said devices,,the coupling between said windings being'low to give ahigh output impedance to one of said waves to prevent outputc urrentfra quency translation.

' '2. A frequency translating circuit comprising a pair ofel'ectric dischargedevices'each "having grid, filament andplate'electrodes,

circuits for associatingfsaid devicesin pushpull relation, means in conjugate relation for supplying'carrier waves and signal Wavesto the input circuit, means for causing intermodulation ofsaid waves in said input circuit, and a transformer having a two section primarywinding connected in the plate circuit, said primary windings having leakage reactance whereby the inter-modulation of said waves in the plate circuits is prevented. 3. A frequency translating circuit c0mprising a pair of'electric discharge devices, each having acathode, an anode and a grid, a divided input circuit therefor having an individual portion connected to each of said grids, respectively, anda common portion connected to said'cathode's, means for supplying waves of different characteristics tosaid individual portions and .said common portion, respectively, to produce input current frequency translation, an output transformer havmg a primary winding connected to the anodeand cathode of each of said devices, thecoupling between said primary windings being low to provide a highimpedance to the'waves supplied tosaid common input portion to prevent output current frequency translation. 4; A frequency translating circuit comprising a three eIe'ctr de electric discharge device, an input circuit therefor, means for supplyingwaves of different characteristics to said input circuit to produce input cur- I rent frequency translation, an output'circuit high impedance at the frequency of at least one of said waves for preventing output current frequency translation.

5. A frequency translating circuit compris-' mg a pair of electric discharge devices each having a cathode, an anode anda grid, a divided input circuit therefor having an individual portion connected to each of said grids, respectively, and a common portion connected to said cathodes, means for supplying waves of diiferent characteristics to said individual and common portions, respectively ,to produce grid current frequency 15 translation, an output transformer having a primary windingconnected to each of said devices, the coupling between'saidprima-ry windings being loose to provide a high impedance to the wave supplied to the common input portion, and an impedance network connected to said transformer and having a high impedance to the wave supplied to the individual input portions.

In witness whereof, I hereunto subscribe 25' CLYDEIRAIKEIITH. I 

